The function
Prevents opening of the solids charging valve while the reactor is above atmospheric pressure, which would blow hot material out of the charging chute onto the operator.
Safe state: Charging valves held closed.
Process safety time: Immediate: the hazard exists as soon as the valve opens. Required response: Interlock acts before the valve can move. Setpoint: Reactor pressure above 0.05 bar g OR vent valve not proven open.
Inputs (illustrative values)
| Group | Voting | λDU /h | λDD /h | λSU /h | β | T1 | PTC | Partial stroke | Type | SC |
|---|---|---|---|---|---|---|---|---|---|---|
| Vent valve open switches ZSO-1601A/B | 1oo2 | 2e-7 | 3e-7 | 2e-7 | 10 % | 1 yr | 95 % | – | B | SC 3 |
| Safety PLC | 1oo1 | 5e-9 | 1e-6 | 0 | 0 % | 10 yr | 99 % | – | B | SC 3 |
| Charging valves XV-1601/1602 | 1oo2 | 8e-7 | 0 | 1e-6 | 10 % | 1 yr | 90 % | – | A | SC 3 |
Mission time 20 years, high demand (PFH). Failure rates are illustrative values written for First Out AI, not taken from any certificate or database.
Result (First Out AI engine v0.3.0)
| Measure | Value |
|---|---|
| PFH | 1.3 × 10⁻⁷ per hour |
| SIL by probability | 2 |
| SIL by IEC 61511 fault tolerance | 3 |
| Systematic capability | SC 3 |
| Achieved SIL | 2 (meets SIL 2) |
| Required PFDavg | – |
| Mean time to spurious trip | 16.7 years |
| Group | Voting | PFDavg | Share | HFT / required | SFF |
|---|---|---|---|---|---|
| Vent valve open switches ZSO-1601A/B | 1oo2 | 1.7 × 10⁻⁴ | 11 % | 1 / 1 | 71 % |
| Safety PLC | 1oo1 | 2.3 × 10⁻⁴ | 15 % | 1 / 1 | 100 % |
| Charging valves XV-1601/1602 | 1oo2 | 1.1 × 10⁻³ | 73 % | 1 / 1 | 56 % |
Engineer's reading
- Charging valves XV-1601/1602 carries 73 % of the PFDavg, so improvements there matter most.
- Demands come with every batch, so the function is verified in high demand mode with PFH; the proof test interval no longer drives the result.
Open this example in First Out AI: SIL verification → Examples → "Batch reactor charging interlock (high demand, PFH)".
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.